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vol. 44 num. 3 lang. eshttp://www.scielo.org.za/img/en/fbpelogp.gifhttp://www.scielo.org.za
Breeding objectives for Holstein cattle in South Africa]]>http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0375-15892014000300001&lng=es&nrm=iso&tlng=es
Well-defined breeding objectives form the basis of sound genetic improvement programmes. Breeding objectives for Holstein cattle in South Africa were developed in the current study. Economic values were calculated for those economically relevant traits that had adequate bio-economic data, namely milk volume, fat yield, protein yield, liveweight, longevity, calving interval and somatic cell score (SCS). A bio-economic herd model for pasture-based and concentrate-fed systems in South Africa was used to calculate economic values by determining changes in profit arising from an independent unit increase in each trait. Alternative payment systems were used from four major milk buyers in South Africa. Relative economic values, standardized to the value of protein yield, were used to compare the relative importance of traits. Protein yield and longevity consistently had positive economic values and the converse was true for liveweight and calving interval. Economic value for volume was positive or negative, depending on whether the payment system rewarded or ignored volume. Sensitivity analysis showed that economic values were reasonably robust against fluctuations in the cost of feed and price of beef; with the exception of fat yield, whose value became negative when feed price exceeded ZAR 3.50. Generally, protein yield was the most important trait, although volume, longevity and SCS were more important in some situations. Calving interval was the least important trait, its value ranging from 4% to 22% of protein yield, although the model may have underestimated its value. Further work should focus on facilitating the wide adoption of these breeding objectives by industry.The relationships between faecal worm egg count and subjectively assessed wool and conformation traits in the Tygerhoek Merino flock]]>http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0375-15892014000300002&lng=es&nrm=iso&tlng=es
Subjectively assessed wool and conformation traits form part of the selection objective in wool sheep enterprises. The present study investigated the genetic, phenotypic and environmental correlations for nematode resistance (using faecal worm egg count (FEC)) with subjectively assessed wool and conformation traits. The Merino sheep flock (consisting of four lines) maintained on Tygerhoek Research Farm was used. Fixed effects of selection line, birth type, sex, age of dam in years, year of birth, and sex*birth year interaction had a significant effect on all subjective traits. At genetic level, log transformed FEC was significantly related to wool oil only at 0.18 ± 0.09, staple formation at 0.29 ± 0.10, and topline at -0.33 ± 0.11. These correlations suggested that sheep with high FEC are likely to have excessive wool oil, thicker and bulkier staples, and lower scores for topline. Selection for resistance to and resilience against nematodes in Merino sheep thus will not result in marked unfavourable correlated responses in the vast majority of these subjective wool and body conformation traits.Effect of pesticides applied in cowpea production on rumen microbial fermentation of cowpea haulms as reflected in in vitro gas production]]>http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0375-15892014000300003&lng=es&nrm=iso&tlng=es
The present study assessed the effect of lambda cyhalothrin, cypermethrin and dimethoate residues in cowpea haulm on microbial fermentation using gas syringes as incubators. The lambda cyhalothrin, cypermethrin and dimethoate were applied at the vegetative, flowering and podding stages of the cowpea at the rate of 2.66 mg/L, 5.14 mg/L and 6.68 mg/L of water, respectively. Dimethoate was detected in the cowpea haulm at the highest concentration of 1.38 mg/kg. The haulm with no pesticide treatment was incubated with media containing rumen fluid, and pesticides were added at concentrations of 40 mg/kg, 80 mg/kg and 120 mg/kg. In vitro gas production was measured at 3 h, 6 h, 12 h, 24 h, 48 h, 72 h and 96 h to estimate the rate of gas evolution. Gas production in general was influenced by pesticide application. In general, gas evolution was reduced by increasing levels of lambda cyhalothrin up to 80 mg/kg. However, an increase in gas accumulation was observed with increasing levels of dimethoate, while the application of cypermethrin yielded no noticeable change in gas production. The study indicates that pesticide residues may function as toxins at concentrations greater than those encountered in the field or lethal dose (LD50) and may inhibit the growth of rumen microbes.